CPCE Computational Fluid Dynamics Theory & Principles 2

Question 1

Which numerical scheme is known for being unconditionally stable for diffusion problems regardless of time step size?

Accepted Answer

Fully implicit (backward Euler)

Answer

The fully implicit (backward Euler) scheme is unconditionally stable for diffusion equations, allowing large time steps without numerical instability.

Question 2

In CFD, the term 'upwinding' refers to:

Accepted Answer

Biasing the differencing stencil in the upstream flow direction

Answer

Upwinding biases the finite-difference or finite-volume stencil to use information from upstream, stabilizing convection-dominated flows.

Question 3

The Peclet number in CFD discretization is defined as the ratio of:

Accepted Answer

Convective transport rate to diffusive transport rate on the mesh

Answer

The cell Peclet number (Pe = u·Δx/ν) compares convective to diffusive transport at the mesh cell level, guiding scheme selection.

Question 4

Which pressure-velocity coupling algorithm uses a staggered arrangement of pressure and velocity unknowns on separate grids?

Accepted Answer

MAC (Marker-and-Cell)

Answer

The MAC method, one of the earliest incompressible solvers, stores pressure at cell centers and velocity at cell faces on a staggered grid.

Question 5

False diffusion in CFD is primarily caused by:

Accepted Answer

Flow not aligned with the grid lines in upwind schemes

Answer

False (numerical) diffusion in upwind schemes is greatest when flow is oblique to the grid, adding artificial smearing of gradients.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE Computational Fluid Dynamics Theory & Principles 2